Mandibular retrognathia in adolescents is an abnormal posterior positioning of the mandible relative to the facial skeleton and soft tissues. This abnormality leads to a number of secondary dental and facial developmental problems, most obviously a shortened lower jaw, which is unable to accommodate all the adult teeth resulting in severe crowding. In many circumstances, this abnormality can be corrected by jaw distraction, a method which involves first dividing a bone through osteotomy, i.e., cutting or fracturing a bone to create two segments separated by a gap or space, and then lengthening the bone member using devices known as distractors. Such distractor devices have fixing members, such as bone plates that are joined to each of the bone segments on opposite sides of the osteotomy, and a distraction or expansion member that allows the distance between the bone plates to be slowly increased over time, thereby allowing new bone growth to occur between the bone segments. The new bone growth increases in dimension until the proper bone length is achieved, at which time the distraction process is halted and the distractor device is removed. By placing an osteotomy cut between the first and second molars of the lower jaw, such jaw distraction surgery pre-emptively creates spaces by distracting the lower jaw forward, thus allowing for the creation of an orthodontic space for later orthodontic alignment of crowded lower dental arches.
When an osteotomy is made in the jaw bone using conventional distractor devices, and particularly the jaw bone of an adolescent, the space available between the closed bone plates of the distractor device located either side of the osteotomy is oftentimes too narrow to effectively fixate the bone plates without interfering with the actual osteotomy cut. As such, the bone plates must be located much further from the osteotomy than is necessary, which requires separation of the bone plates, and subsequently shortens the possible maximum displacement of the bone plates and thus the lengthening of the jaw bone that can be achieved through distraction. Also, because the osteotomy is made between the first and second molar teeth, bone plate fixation may impact upon, in particular the first molar tooth, compromising it, or, by virtue of attempting to fixate too long a forward bone plate before the osteotomy, displaces the line of the distraction vector below the occlusal plane of the lower jaw.
The present invention seeks to provide a distractor device and a method for distracting a jaw bone which will overcome or substantially ameliorate at least some of the deficiencies of the prior art, or to at least provide an alternative.
It is to be understood that, if any prior art information is referred to herein, such reference does not constitute an admission that the information forms part of the common general knowledge in the art, in Australia or any other country.